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排序方式: 共有138条查询结果,搜索用时 31 毫秒
111.
Adeline Loyau Michel Saint Jalme Cécile Cagniant Gabriele Sorci 《Behavioral ecology and sociobiology》2005,58(6):552-557
The evolution of multiple sexual traits remains controversial and poorly understood in evolutionary biology. In many bird species, males exhibit complex courtships involving feather ornaments and behavioral display. Multiple traits may convey information on the genetic and phenotypic quality of males. In particular, fixed characters, such as feather ornaments (produced once a year during the annual molt in many bird species) might convey information about past male condition (at the time of trait development); whereas flexible traits such as behavioral displays should be sensitive to present condition. Here we show that both flexible behavioral displays and fixed feather ornaments of peacocks, used by females to choose a mate, honestly reflect health status. Correlative data showed that peacocks with high display rate (the number of behavioral displays per hour) and a large number of tail eyespots had low levels of circulating heterophils, suggesting better health status. Experimental activation of the immune system, through LPS injection, significantly reduced display rate compared to a control group. However, the sensitivity of a male display rate to the immune challenge was dependent on the number of tail eyespots: males with higher number of tail eyespots were better able to cope with the experimental immune challenge, and maintained their display rate at levels closer to the levels performed before the immune activation. These results are consistent with the idea that multiple signaling might enhance information reliability. 相似文献
112.
113.
This paper clarifies how polymers are dealt with under the Directive 67/548/EEC. Polymers are a particular group of substances under the Directive 67/548/EEC [1] and amendments [2,3] as they are not listed in the European INventory of Existing Commercial chemical Substances (EINECS [4]) which otherwise lists all substances which were on the European Community Market between 1 January 1971 and 18 September 1981, the ‘existing substances’. Instead, in EINECS polymers are registered under their ultimate building blocks. With the 6th amendment to the Directive [2] polymers became notifiable substances if containing 2% or more of new substance(s) (i.e. as a general rule substances not listed in EINECS), and the reporting criteria were used as definition. With the 7th amendment to the Directive [3] an exact definition was introduced and a special test package, given in Directive 93/105/EEC [5], was designed for polymers to take into account their particular properties. Changing the definition of polymers created a group of substances which under the 6th amendment had been defined as polymers, and could no longer be regarded as polymers under the 7th amendment, the No‐Longer‐Polymers. 相似文献
114.
115.
This study evaluated the effects of time of day, ambient temperature, and relative humidity on mother-infant interactions
in captive Japanese macaques (Macaca fuscata). Unlike time of day and relative humidity, temperature influenced mother-infant interactions. Even though total time spent
in ventroventral contact did not change, lower temperatures were associated with greater attempts by the infants to maintain
contact with their mothers and with more frequent maternal rejection. Effects of temperature on mother-infant interactions
were not mediated by the effects of temperature on mothers' general activity. These results are interpreted in light of the
different thermoregulatory needs of mothers and infants, and highlight a previously neglected cause for mother-infant conflict.
Received: 23 June 1997 / Accepted after revision: 28 March 1998 相似文献
116.
Manoli G Chambon JC Bjerg PL Scheutz C Binning PJ Broholm MM 《Journal of contaminant hydrology》2012,131(1-4):64-78
A numerical model of metabolic reductive dechlorination is used to describe the performance of enhanced bioremediation in fractured clay till. The model is developed to simulate field observations of a full scale bioremediation scheme in a fractured clay till and thereby to assess remediation efficiency and timeframe. A relatively simple approach is used to link the fermentation of the electron donor soybean oil to the sequential dechlorination of trichloroethene (TCE) while considering redox conditions and the heterogeneous clay till system (clay till matrix, fractures and sand stringers). The model is tested on lab batch experiments and applied to describe sediment core samples from a TCE-contaminated site. Model simulations compare favorably to field observations and demonstrate that dechlorination may be limited to narrow bioactive zones in the clay matrix around fractures and sand stringers. Field scale simulations show that the injected donor is expected to be depleted after 5 years, and that without donor re-injection contaminant rebound will occur in the high permeability zones and the mass removal will stall at 18%. Long remediation timeframes, if dechlorination is limited to narrow bioactive zones, and the need for additional donor injections to maintain dechlorination activity may limit the efficiency of ERD in low-permeability media. Future work should address the dynamics of the bioactive zones, which is essential to understand for predictions of long term mass removal. 相似文献
117.
In the present research mortar pastes obtained by replacing a commercial cement with the equivalent mass of 5, 10, 20 and 30 wt.% of fly ash or bottom ash from fir chips combustion, were prepared and rheologically characterized. It was observed that the presence of ash modifies their rheological behaviour with respect to the reference blend due to the presence, in the ashes, of KCl and K2SO4 which cause precipitation of gypsum and portlandite during the first hydration stages of the pastes. Hydrated materials containing 5 wt.% of ash display compression strength and absorption at 28 d of same magnitude as the reference composition; conversely, progressive increase of ash cause a continuous decline of materials performances. Conversely, samples tested after 180 d display a marked decline of compression strength, as a consequence of potassium elution and consequent alkali-silica reaction against materials under curing. 相似文献
118.
Frank D. Belschak Gabriele Jacobs Steffen R. Giessner Kate E. Horton P. Saskia Bayerl 《组织行为杂志》2020,41(9):830-850
Large-scale, long-term change initiatives take time to unfold, which can be a source of uncertainty and strain. Investigating the initial 19 months of a large-scale change, we argue that during these stages, employees' change-related beliefs become more negative over time, which negatively affects their work engagement and, ultimately, increases their turnover intentions. Furthermore, we investigate the impact of a trait, Machiavellianism, on change reactions and propose that employees high in Machiavellianism react more negatively during change processes as they are especially susceptible to uncertainty and stress. We test our (cross-level) moderated mediation model in a three-wave longitudinal study among employees undergoing a large-scale change (T1: n = 1,602; T2: n = 1,113; T3: n = 759). We find that employees' beliefs about the impact and value of the change are indeed negatively related to change duration and that decreases in these perceptions come with a decline in engagement and increases in turnover intentions. Moreover, employees high in Machiavellianism react more strongly to a deterioration in change-related beliefs, showing stronger reductions in engagement and stronger increases in turnover intentions than employees low in Machiavellianism. Our study offers explanations for the negative effects of large-scale changes including an explanatory factor for disparate employee reactions to change over time. 相似文献
119.
DGT use in contaminated site characterization. The importance of heavy metal site specific behaviour 总被引:1,自引:0,他引:1
The objective of this study is to provide an insight into the techniques for measuring the lability of heavy metals in solid-phase pool of soils in order to assess the environmental risk arising from pollution. The technique of diffusive gradients in thin films (DGT) and a sequential extraction procedure were used to quantify the labile pools of Cu, Fe, Mn and Ni. These results were compared to metal concentrations in groundwater, measured directly using the in situ piezometers, and to the total concentration of metal in the soils. High concentrations of metal in the directly analysed soil solution compared to DGT measurement were attributed to the presence of colloidal metal. The use of DGT allowed only to calculate leaching parameters of the free ions and labile fractions of the metals. For this reason DGT technique needs preliminary investigation on metal speciation in soil solution before its application as a good tool in the characterization procedure of contaminated sites. 相似文献
120.
Seasonal variation in the relationship between cellular immune response and badge size in male house sparrows (Passer domesticus) 总被引:7,自引:2,他引:5
Guillermo Gonzalez Gabriele Sorci Florentino de Lope 《Behavioral ecology and sociobiology》1999,46(2):117-122
The immunocompetence handicap hypothesis postulates that secondary sexual traits are honest signals of male quality because
steroid hormones (such as corticosteroids and sex steroids), which are supposed to favor the development of secondary sexual
traits, may also have immunosuppressive effects. Certain secondary sexual traits are not only used as mate choice signals
but also play a role as badges of status. In the house sparrow (Passer domesticus), males have a bib of black feathers which is used both as a signal of social status in male-male interactions and by females
when choosing a mate. We investigated the relationships between bib size and cellular immune response in male house sparrows
during and outside the reproductive season. Males with large badges were found to have lower levels of immunocompetence, as
assessed using a T-cell-mediated immunity assay, during the reproductive season, as predicted by the immunocompetence handicap
hypothesis. Conversely, in November, the correlation between badge size and cellular immune response was positive, possibly
reflecting the better access to trophic resources of large-badged dominant males in winter flocks.
Received: 24 September 1998 / Received in revised form: 2 February 1999 / Accepted: 14 February 1999 相似文献